Here is a Savage 210 with bottom of action opened up
toward the back, to take cases with 3.5" overall length.
Slug Warrior on Shotgun World did it. Is similiar job the
Brett in MN did, but he made his opening 3.7". I measured
mine and they can be opened to 3.95". They also milled
the rim guides back for controlling case feeding on longer
cases. Ed